1. Field of the Invention
This invention relates to a spring forming machine, more particularly to a driving mechanism for moving a cutter or pitch control rod in a spring forming machine.
2. Description of the Related Art
Referring to FIG. 1, a conventional spring forming machine 1 is shown to include a cutting device 10, a pitch control device 11, a pair of feeding rollers 12, two bending devices 13, and a positioning horizontal cylinder 14. A metal strip 15 is pushed by the feeding rollers 12 to extend between the positioning horizontal cylinder 14 and the bending devices 13, thereby forming a turn around the positioning horizontal cylinder 14. A pitch control rod 110 of the pitch control device 11 effects a vertical movement, and has an oblique top surface that presses against the metal strip 15 to define a predetermined pitch for a coiled spring to be formed. By adjusting the pitch control device 11, coiled springs of different pitches can be formed. After a coiled spring of a predetermined length has been formed, a cutter 100 of the cutting device 10 moves downward to cut off the coiled metal strip 15.
Each of the cutting device 10 and the pitch control device 11 has a driving mechanism. Referring to FIG. 2, the driving mechanism 2 is shown to include a slide plate seat 21 which is adapted to be fixed on a machine frame (not shown), a slide plate 22, a holder 23, a power source 24, and a linkage assembly 25. The holder 23 is used to hold the cutter 100 (see FIG. 1) or the pitch control rod 110 (see FIG. 1) thereon. The linkage assembly 25 includes a connector 250, a swing arm 251 coupled with the slide plate 22 by means of the connector 251 at an end thereof, a shaft 252 connected fixedly to the other end of the swing arm 251 at an end thereof, a swing arm 253 connected fixedly to the other end of the shaft 252 at an end thereof, a slide member 254 attached to the other end of the swing arm 253, and a rotary wheel 255. The shaft 252 is journalled on the machine frame (not shown). The slide member 254 is received slidably in an irregular-shaped guide slot 256 in the rotary wheel 255. The power source 24 rotates the rotary wheel 255 to move the slide plate 22 within the slide plate 21. The aforementioned driving mechanism 2 suffers from the following disadvantages:
(1) Because the linkage assembly 25 consists of numerous members 250, 251, 252, 253, 254, 255, it is difficult to control accurately the pitch of the spring to be formed.
(2) Referring to FIG. 3, because the cutter 110 (see FIG. 1) moves on the machine frame (not shown) along a straight path, a sharp projection 152 is present on an end surface 151 of a coiled spring 150, which is formed by the conventional spring forming machine 1 (see FIG. 1).